Field Report: Wheatstone Bridge

In 2000, Cumulus began building a new facility for its stations in Houston, which is one of the company's largest markets. This project would later become a showcase for the entire company. The primary design goal was that versatility and reliability would be emphasized on the studio end of the project. We also wanted the studio to be state-of-the-art. Likewise, I cover several stations in the region and having to drive a couple of hours to fix problems isn't practical, so having flexible and reliable studios was important. The goal was to have sufficient backup plans in place to prevent extra trips between Beaumont, TX, and Houston. The company needed an audio router to link as many inputs as possible — and it had to be easy to use. We also wanted to keep as much of the audio in the digital domain as possible, while still being able to seam-lessly integrate the existing analog sources into the digital infrastructure around which our facility was built.

An important part of this infrastructure was the Wheatstone Bridge digital audio network router. This unit allows the user to interconnect almost every source and destination in the facility and allows selection with the turn of a dial or via TCP/IP. The basic system consists of a power supply and 4RU main card cage. The cage design offers a rear backplane that accepts the input and output connector cards, while the processor cards slide easily into the front. This design seems to be ideal for switching cards between each other for troubleshooting, or switching components to replace a dead audio source. The backplane is a dual-sided connection point for the front and rear components. The rear I/O card is inserted to match with its corresponding processing card in the front. Cards can easily be swapped. The backplane connectors are fixed and are the only potential point of failure.

Performance at a glance
  • As many as 2,048 input and output signals
  • Interconnects with Wheatstone consoles
  • Variety of processing modules and I/O modules
  • Fiber optic or CAT-5 multi-unit connection
  • Sample rate converters on all digital inputs
  • Reduces wire and cable needs
  • When first installed, we had a problem with one of the backplane connectors. When the audio from our satellite receiver disappeared, we tracked the problem down to the backplane. A call to Wheatstone support resulted in a manufacturer tech coming to visit us to replace the component. The problem was an isolated case and we were able to easily work around it.

    Deep integration

    The design plan included Wheatstone D-5000 digital consoles in each studio, which would interface directly with the router. An optional console module makes routing control accessible and easy. The router and console interface updates the console channels' LED labels to indicate the selected sources, greatly increasing user friendliness. In addition, the router is smart enough to block changes when the fader is turned on, thereby eliminating the accidental switch of a source while it is still live.

    Two types of audio input cards can be used for AES-3 digital or analog 24-bit A-D input. In addition, 24-bit digital or 24-bit D-A analog output cards are available. The AES-3 cards have sample-rate converters on every input. The systems can accept up to 2,048 discrete analog and digital signals and switch them to any of 2,048 separate outputs. A system can consist of a single cage, or several cages can be linked to form a larger system. Cages can be separated and network audio through bi-directional fiber optic links or a single CAT-5 connection.

    The classic method of feeding audio sources through distribution amplifiers and then running these feeds to every studio, rack room, production and news room in the building is labor-intensive and requires significant amounts of hardware. By using the router for audio interconnection we were able to substantially save costs and greatly reduce the time needed for installation.

    Sources and destinations can be controlled through dedicated control panels such as this one, or through the communications port, allowing consoles and automation systems to make changes.

    The audio router offers many benefits. When our main T1 STL link to our transmitter failed, the backup ISDN codec tried to dial but was unsuccessful. I would have had to drive two hours to rearrange some equipment or create a temporary installation. Instead, the announcer routed the air studio program audio to an ISDN codec in another room, which got the station back on the air without any new rewiring.

    The system also allowed us to maintain a completely digital audio chain. The station's music is ripped from a CD, played through the AES-3 output of the automation system and routed digitally until it becomes RF. The router even converted the analog sources, such as the Starguide receivers, into digital.

    The system was fairly easy to install, too. With CAT-5 cable now being a common part of any businesses wiring, interconnecting the router to the consoles and the setup computer is a snap. The consoles connect to the router via RS-485. The Ethernet connection connects to a TCP/IP network to allow communication via the setup software on any computer on that network. This software shows a visual overview of the system routing and allows the user to make changes and restrict or permit specific routing. One example would be to restrict routing a device's output to its own input.

    We ordered our system with a number of analog and digital inputs and outputs that can be upgraded when we need more. It came with the pigtail cable assemblies pre-wired. This allowed us to run the wires and punch them down to block without having to solder connectors.

    Davis is chief engineer for Cumulus Broadcasting in Houston/Beaumont, TX.


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    Editor's note: Field Reports are an exclusive Radio magazine feature for radio broadcasters. Each report is prepared by well-qualified staff at a radio station, production facility or consulting company.

    These reports are performed by the industry, for the industry. Manufacturer support is limited to providing loan equipment and to aiding the author if requested.

    It is the responsibility of Radio magazine to publish the results of any device tested, positive or negative. No report should be considered an endorsement or disapproval by Radio magazine.

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